The effects of an acute dose of ethanol (75 mmol/kg body weight; ip) on protein synthesis were investigated in the small intestine of the rat (n = 6). Control rats (n = 6) were injected with isovolumetric 0.15 mol/l NaCl, ip. After 2.5 h, fractional rates of protein synthesis (defined as the percentage of tissue protein renewed each day by synthesis and RNA efficiencies (defined as the amount of protein synthesised per unit RNA) were measured with a large flooding dose (0.3 Ci/mol; 150 mmol/l; 150 mumol/100 g body weight; iv) of [4(3)H]-phenylalanine. Rats were killed 10 minutes after injection of the isotope and portions of the small intestine were rapidly dissected and frozen. Tissues and plasma were processed for phenylalanine specific radioactivities to obtain fractional rates of protein synthesis or protein synthesis rates relative to RNA. Rates of protein synthesis in mixed tissue proteins fell approximately 15-25% (p ranged from less than 0.005 to greater than 0.05), in response to acute ethanol dosage. The decrease in the synthesis rates of the cytoplasmic protein fraction was similar (p less than 0.025). Proteins extracted from the smooth muscle contractile apparatus, however, showed a greater response to ethanol--that is, 40-50% inhibition in protein synthesis (p less than 0.001). It is therefore possible that the functional disturbances in the ethanol-exposed gut may be because of changes in smooth muscle protein turnover with decreased amounts of contractile apparatus.
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